The present invention relates to a support member for photographic printing paper, and in particular to a support member for photographic printing paper with high resolving power.
In recent years, a support member for waterproof photographic printing paper, both sides of which are coated with polyolefin such as polyethylene for rapid development processing of photographic printing paper. However, photographic image obtained from the photographic printing paper using polylefin-coated paper is disadvantageous in that resolving power is not very high.
This disadvantage is attributable to the fact that light scatters within polyolefin layer because white pigment mixed in the polyolefin layer, which is coated on the surface of the polyolefin-coated support member to contact with photosensitive silver halide emulsion is not sufficient in quantity and its shielding effect is not strong enough.
Normally, titanium oxide is used as the white pigment. Improvements of surface coating of titanium oxide to increase the quantity filled into polyolefin have been disclosed in Japanese Patent Laid-Open Publication No. 55-108658 and Japanese Patent Laid-Open Publication No. 57-35855, etc., and simultaneous use with other pigment is disclosed in Japanese Patent Publication No. 49-27046. In any case, however, filling quantity of titanium oxide is up to 15 weight % at the highest.
In this respect, methods are described in Japanese Patent Publication No. 57-53937 and Japanese Patent Laid-Open Publication No. 57-64235, by which a white pigment layer comprising white pigment and hydrophilic colloid solution is placed on a film or a resin-coated paper, and a photosensitive emulsion layer is placed on the white pigment layer. In the photographic printing paper using the support member disclosed in these patents, binder of the white pigment layer is hydrophilic and absorbs development processing solution or water, and it is disadvantageous because drying is delayed compared with the photographic printing paper using ordinary polyolefin-coated paper as the support member.
A method to coat an aqueous emulsion comprising binding agent and pigment is disclosed in Japanese Patent Laid-Open Publication No. 50-44818. However, when aqueous material is coated, drying is delayed and high-speed processing is not achievable, or drying zone must be extremely enlarged. Further, when emulsion is used, mechanical stability of the emulsion is reduced and uniform coating is not accomplished when gravure roll or bar are coated continuously.
To overcome the above problems, Japanese Patent Laid-Open Publication No. 59-200234 discloses a method, by which a binder soluble in organic solvent and white pigment are coated.
As the binder soluble in organic solvent, there are polyvinyl chloride, vinyl chloride-acetic acid copolymer, polyvinyl acetate, or polystyrene. However, mere use of such binders leads poor binding between base material and binder layer containing white pigment or the binding between layer and silver halide emulsion layer. Thus, it is necessary to perform surface treatment such as corona processing or lining in advance on the base material or on the surface of the binder layer. This results in more complicated manufacturing process and higher cost. Also, the use of polymer containing vinyl chloride causes discoloring to yellow as time elapses or by heat.
It is a first object of the present invention to provide a support member for photographic printing paper, by which a photographic image with high resolving power can be obtained.
It is a second object of the present invention to provide a support member for photographic printing paper, which has high bonding property with base material or with silver halide emulsion layer and is easier to manufacture.
It is a third object of the present invention to provide a support member for photographic printing paper, which is not easily discolored as time elapses or by heat.